3.1.2 Carbohydrates Flashcards
what are monosaccharides?
The individual sugar monomers from which larger carbohydrates are
made.
what are disaccharides?
formed by the condensation of two monosaccharides
what are 3 common types of monosaccharides and examples?
triose - glyceraldenyde
pentose - deoxyribose
hexose - glucose, fructose, galactose
what is an isomer?
same molecular formula but different structural formula (arrangement of atoms)
what is the difference between alpha glucose and beta glucose?
in alpha glucose, the hydroxyl group in carbon atom 1 is below the hydrogen whereas in beta glucose the hydroxyl group in carbon atom 1 is above hydrogen
what is a glycosidic bond?
A bond between two monosaccharides formed in a condensation reaction.
how is maltose formed?
condensation of two glucose molecules
how is sucrose formed?
condensation of a glucose molecule and a fructose molecule
how is lactose formed?
condensation of a glucose molecule and a galactose molecule
what is the process of the benedicts test?
- add 2cm^3 of test solution
- add an equal amount of benedict’s solution
- heat in a water bath
what is a positive test of benedict’s solution?
brick red precipitate
what is a negative test of benedict’s solution?
blue
how do you know the concentration of a reducing sugar?
- high conc. = further colour change e.g brick red
- compare to different solutions, or more accurately, filter solution and weigh precipitate
- or remove precipitate and use a colorimeter to measure absorbance of remaining benedict’s reagent
how do you test for non-reducing sugars?
- add dilute HCl to the test solution + carefully heat in a water bath
- you then neutralise it by adding sodium hydrogencarbonate
- retest the mixture using the test for reducing sugars (Benedict’s solution) - the non-reducing sugar will have been hydrolysed into monosaccharides which are reducing sugars
what is an anomeric carbon?
carbon of the carbonyl group present in the straight chain of the sugar
why do non-reducing sugars not reduce benedict’s solution?
sugars reduce benedict’s solution when the anomeric carbon atom is made available to reduce the copper ions in the solution
- e.g the anomeric carbon atom of glucose is 1, for fructose is 2 - sucrose is a 1-2 glycosidic bond so the anomeric carbon atoms have been taken up
why are reducing sugars called reducing?
- Cu2+ ions are reduced to Cu+ in benedicts solution - which form copper (I) oxide in the presence of alkaline sodium hydroxide
what does polysaccharide mean?
many sugars
what monosaccharides are polysaccharides made of?
alpha-glucose OR beta-glucose
what’s the purpose of starch?
plants store excess glucose as starch (starch can be hydrolysed back into glucose when plants require glucose for energy via respiration)
- mixture of two polysaccharides - amylose and amylopectin - make up starch
- it is also insolutuble - no osmotic effect (doesnt cause water to enter cell by osmosic which could make cell swell, this is good for storage)
- it is a large molecule - cannot diffuse out of cells bcause it can’t pass the cell membrane
what is amylose?
- alpha-glucose, 1-4 glycosidic bonds
- long, unbranched chain
- coiled structure - compact, stores lots of glucose
what is amylopectin?
- alpha-glucose
- 1-4 and 1-6 glycosidic bonds meaning it’s branched - allows enzymes to hydrolyse the glycosidic bonds easily to rapidly release glucose for respiration which released energy quicker
what is glycogen?
- store of excess glucose in animals
- alpha-glucose
- 1-4 and 1-6 glycosidic bonds
- coiled - compact - good for storage
- more highly branched than starch (allows enzymes to hydrolyse the glycosidic bonds easily to rapidly release glucose for respiration which released energy quicker)
- insoluble - no osmotic effect
- large molecule - cannot diffuse out of cells bcause it can’t pass the cell membrane
what is cellulose?
- found in plants (make up cell wall)
- insoluble - no osmotic effect
- beta-glucose, 1-4 glycosidic bonds - hydroxyl groups on c1 and c4 are too far to react, so every other beta-glucose is inverted 180º (upside down).
- form long, straight, unbranched cellulose chains
- cellulose chains linked by many hydrogen bonds (weak by itself, strong + rigid when there’s many)
- cellulose chains join to form microfibrils which join to form macrofibrils which combine to make strong cellulose fibres in the cell wall of plants
- provide structural support of cells
how do you do the iodine test for starch?
- add 2cm^3 of sample
- add few drops of iodine in potassium iodide
what is a positive test of the iodine test?
blue-black
what is a negative test of the iodine test?
orange-brown
